The present invention relates to an apparatus for maintaining proper operating temperatures for electronic instrumentation and the like enclosed therein. In particular, it relates to an apparatus in which a vaporizable cooling medium is employed to carry heat away from the electronic equipment in the form of vapor which is absorbed in a canister filled with a vapor absorbent chemical, so as to form a totally self-contained equipment cooling system. The present invention is particularly applicable to the cooling of bore hole instrumentation used in oil well logging.
In modern oil exploration technology, bore holes extending as deep as 20,000 feet and deeper are becoming quite common. Additionally, ever-increasingly sophisticated instrumentation packages are lowered into the oil well bore hole to gather chemical, geological, nuclear, sonic and other forms of information in attempts to evaluate the prospects for oil, gas or other mineral recovery from the underlying rock strata. However, temperatures within the bore hole can be as high as 225.degree. C. However, temperatures between about 150.degree. C. and about 200.degree. C. are more commonly encountered. Since modern electronic circuits begin to exhibit problems at temperatures between about 80.degree. C. and 100.degree. C., the use of electronic devices, such as conventional silicon integrated circuits and memory chips, is either totally excluded or is at least significantly impaired. The problem of cooling the bore hole instrumentation package is seen to be a significant one in light of the fact that the equipment one is seeking to cool may be about four miles away, underground. Accordingly, the desirability of some form of self-contained cooling system for this instrumentation package is highly desirable.
The problem of cooling instrumentation packages in oil well logging systems is appreciated in U.S. Pat. No. 3,038,074, issued June 5, 1982 to S. A. Scherbatskoy. However, there is no provision therein which limits the vaporization of the cooling fluid to those times for which it is most desirable, namely, when the temperature within the package exceeds about 50.degree. C. In the Scherbatskoy apparatus vaporizing liquid continuously evaporates from the reservoir thus shortening the length of time that the package is operable under bore hole thermal conditions. Moreover, Scherbatskoy is unappreciative of the particular advantages of calcium oxide, sodium oxide or Zeolite as coolant absorbent materials.